Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface in accordance with my design.

The broken lines shown in the drawing illustrate a mobile device and portions of the display screen or portion thereof with a graphical user interface that forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 